1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device.
2. Description of the Related Art
With the increasing integration degree of semiconductor devices, ensuring an appropriate capacitance value for capacitors in memory devices has been increasingly difficult. To ensure the appropriate capacitance value, high dielectric-constant films comprising dielectrics with high dielectric constants have been developed.
Furthermore, for MOS transistors, efforts have been made to reduce the thickness of a gate insulating film in order to improve driving capability. However, the reduction in the thickness of the gate insulating film involves a disadvantageous increase in gate leakage and is thus limited. Consequently, high dielectric-constant films have been developed which allow an effective film thickness to be reduced without the need to reduce the physical film thickness.
The developed high dielectric-constant films comprise metal oxides such as HfO2, ZrO2, and Al2O3, oxides such as silicate and aluminate, and ternary oxides such as BST and STO. Related techniques are disclosed in Japanese Patent Laid-Open Nos. 2008-28051 and 2002-314072.
Japanese Patent Laid-Open Nos. 2004-214602 and 2002-314072 disclose methods for suppressing oxidation of a lower electrode. For example, Japanese Patent Laid-Open No. 2004-214602 discloses a method for suppressing oxidation of a lower electrode in an HfO2 film. The method comprises forming, on the lower electrode, a stack structure of an Al-rich HfO2—Al2O3 mixed film and an Hf-rich HfO2—Al2O3 mixed film or a stack structure of an Al2O3 film and an Hf-rich Al2O3 mixed film to suppress the oxidation of the lower electrode.